1. Field of the Invention
The invention relates to a device for comminuting material, in particular, material in the form of trunk wood and residual wood as well as wood material combined to a packet, comprising a comminution chamber surrounded by a rotary blade ring into which the material is fed in the axial direction, wherein, for the purpose of comminution, the rotary blade ring is movable in the radial direction against an abutment projecting axially into the comminution chamber.
2. Description of the Related Art
Devices of the aforementioned kind for comminution of material are known, for example, from DE 35 05 077. Such devices have a horizontally movable carriage on a stationary frame. On the carriage a comminution apparatus is arranged which is comprised substantially of a rotary blade ring surrounding a comminution chamber. The cutting edges of the comminution tools project with a short projecting length from the inner side of the rotary blade ring into the comminution chamber. For providing an abutment during the comminution process, the device of the aforementioned kind has a stationary abutment which projects axially into the comminution chamber.
For comminuting the feed material, the feed material is fed axially into the comminution chamber and secured within as well as outside of the comminution chamber. By horizontally moving the carriage and thus also the rotating blade ring, the material is compressed between the counter abutment and the rotary blade ring and at the same time comminuted by the cutting edges of the rotary blade ring. By means of the continued advancing movement of the rotary blade ring in the direction toward the abutment, the pressing force required for comminution is maintained. After completion of a working stroke, with which a section of the feed material corresponding to the depth of the comminution chamber has been processed to chips or cuttings, the carriage together with the rotary blade ring moves back into its initial position, and the material is then advanced farther by the length of a further section into the comminution chamber. In this way, a cycled comminution of the feed material by the depth of the comminution chamber, respectively, is achieved.
Such devices have proven very successful in practice. Problems occur only when the material is contaminated by hard foreign bodies. The hard foreign bodies can be, for example, broken-off parts of woodworking tools of previous processing stations or shrapnel dating back to the World Wars I and II that have penetrated into the trunk wood. They are engaged during the course of the comminution of the material by the comminution tools of the rotary blade ring and cause increased wear, and, in more serious cases, even destruction of machine parts.
In order to overcome this problem, it has been suggested to test the material with regard to foreign bodies by means of detectors. According to this method, feed material contaminated by foreign bodies can already be sorted out prior to processing. However, experience has shown that, actually, this is achieved only unsatisfactorily so that a residual risk is still present for the devices of the aforementioned kind.
In order to prevent this residual risk, it is also already known to provide a device of the aforementioned kind with a monitoring and control system. It monitors, on the one hand, the drawing of current at the drive side of the device and, on the other hand, the operating pressure of the cylinder-piston unit which provides the feed action of the rotary blade ring. A sudden increase of the current draw and/or a sudden increase of the operating pressure of the cylinder-piston unit indicates a foreign body within the feed material. In order to protect the comminution device, the cylinder-piston unit which provides the feed action is then switched to a pressureless state for reducing the pressing force between the comminution tool and the foreign body. Parallel to this, braking and stopping of the rotary blade ring can be realized.
Both alternatives, however, have the disadvantage that a reaction in response to the signal indicating the foreign body can be provided only with some temporal delay. This is caused, on the one hand, by the large mass of the rotating blade ring and the resulting great kinetic energy as well as the inertia of the hydraulic advancing or feeding system. Possibly, the rotary blade ring cannot be protected from damage as a result of the temporally delayed counter measures.
It is an object of the present invention to development the devices of the aforementioned kind such that feed material contaminated with foreign bodies cannot cause any damage during operation of such a device.
In accordance with the present invention, this is achieved in that at least the effective surface of the counter abutment facing the feed material is moveably supported so that, upon surpassing a predetermined value of the pressing force caused by the advancing of the rotary blade ring, at least the effective surface of the counter abutment will yield to or perform an escape movement relative to the rotary blade ring.
The invention takes an entirely new direction for solving the aforementioned object in that it no longer changes the pressing force acting on the comminution blades indirectly via the control of the cylinder-piston unit driving the carriage but reduces directly the pressing force required for an effective comminution. This is realized by providing an escape movement of the counter abutment in the advancing direction of the rotary blade ring.
With this inventive concept, the pressing force onto the comminution tools is reduced directly without any intermediate action so that a very fast response for protecting the device according to the invention is realized. This escape movement of the counter abutment is effected by the pressing force which is present within the comminution chamber so that for this purpose no additional force expenditure is required. Moreover, the parts which are to be moved for damage control have relatively small dimensions with a corresponding minimal weight so that their minimal inertia further improves a quick response.
The escape movement of the counter abutment can be realized in different ways. Preferred is a parallel movement of the surface of the counter abutment facing the rotary blade ring in the advancing direction or feed direction of the rotary blade ring.
As a result of the specific weight and primarily of the entrainment effect of the comminution tools, the foreign bodies will collect preferably in the area of the counter blade, i.e., in the lower area of the comminution chamber. An escape movement of the effective surface of the counter abutment in this area can also be made possible by a pivot movement of the effective surface about an axis extending horizontally in the upper area of the counter abutment.
A preferred embodiment of the invention provides for a substantially two-part configuration of the counter abutment. In this connection, on a stationary part of the counter abutment, which receives the abutment forces occurring during operation, a movable attachment is provided which is facing directly the feed material. This embodiment reduces the number and the weight of the movable parts of the counter abutment to a minimum so that this embodiment ensures very short response times. The movability between the rigid part and the attachment is ensured by guide elements which are aligned in the advancing direction.
In other preferred embodiments the counter abutment is a rigid or stiff structure which is movably supported on the remaining stationary structure of the device outside of the comminution chamber. In this way, larger moving masses are obtained but this configuration has the advantage of an improved accessibility of the moveable support and the drive. A further advantage of this configuration is based on the simple configuration of the part of the counter abutment projecting into the comminution chamber which can be formed with minimal thickness as a result of its unitary configuration. In this connection, for identical rotary blade ring size an enlargement of the comminution chamber results so that it can receive and process more feed material. In this embodiment, the movability of the counter abutment is realized by means of a sliding support on the stationary structure of the device.
Further advantages result from a combination of the aforementioned embodiments in which a counter abutment with attachment is additionally moveably secured by means of its support arm on the stationary structure external to the comminution chamber. The two systems for providing an escape movement can cooperate in this connection such that a first quick escape movement is realized via the attachment on the support arm and a further escape movement is realized by a movement of the support arm.
In a simplified embodiment of the invention, the counter abutment is secured by means of a spring element in its nominal or working position. The spring force corresponds in this connection to a predetermined value of the pressing force for which the presence of foreign bodies does not yet cause appreciable damage. Upon surpassing this pressing force value, the counter abutment moves back with compression of the spring element and prevents greater damage.
An especially preferred embodiment of the invention has a monitoring and control system as well as at least one cylinder-piston unit which secures the counter abutment in its nominal or working position. Upon reaching a predetermined value of the pressing force, which signals the presence of foreign bodies at the comminution tools, the cylinder-piston unit is switched to a pressureless state in order to thus initiate an escape movement of the counter abutment.
This embodiment has the advantage that the starting point for the escape reaction can be controlled very precisely. Since the feed material to be comminuted is present in a compressed state within the comminution chamber, the switching of the cylinder-piston unit into a pressureless state provides a relaxation possibility for the feed material which effects the restoring force for the escape movement of the counter abutment.
According to further embodiments of the invention, this restoring force can be actively enhanced for accelerating the escape movement in that double-acting cylinder-piston units and/or pre-stressed spring elements are used.